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Information from NOAA’s Satellite Fleet Helps Point to How Warming Ocean Temperatures Impact Marine Food Web and Whale Distribution

Wednesday, February 12, 2020

NOAA's satellites utilize microwave and infrared radiometers to measure sea surface temperatures, giving researchers valuable clues about the ocean—and welfare of animals—that lie beneath its surface. 

Photo of Whale

Instruments such as the VIIRS on the Suomi-NPP satellite are designed to collect information about the ocean as it emits radiation in different wavelengths, which can change based on the temperature of any particular section of the sea’s surface. However, how does what happens on the surface affect animals such as whales, which regularly inhabit spaces that are up to 10,000 feet deep?

Satellites in NOAA’s fleet provide metrics for understanding habitat requirements of fish, seabirds, and whales. They record surface temperatures and ocean features (e.g., fronts, circulation features) of the water over time, which are used by NOAA scientists who are making their own measurements with instruments such as buoys and ships of opportunity. Sea surface anomaly maps, created by NOAA National Centers for Environmental Information (NCEI), integrate satellite sensor information and provide visual references that correspond to the biophysical changes in the food web below the sea’s surface. 

For starters, sea surface temperature influences organisms that inhabit the ocean surface layer, including those that form the base of the ocean food web—phytoplankton. In 2014, satellites and on-the-ground researchers observed persistent warming of the north Pacific Ocean, just off of the West Coast of the continental U.S. This marine heatwave event, known as “The Blob”, created ideal conditions for toxic algal blooms which impacted marine wildlife and fisheries. The warming event and algal bloom altered the balance of conditions for marine wildlife, causing whales and others in the food web—such as krill, shrimp, and other forage fish species—having to contend with elevated harmful compounds in the water. As a result, there was an unusual die-off of larger cetaceans such as fin and humpback whales

Satellite-derived maps monitored the climax of The Blob’s effects in 2014-2016 as it moved from the Pacific Northwest to Mexican waters; krill (a major food source for baleen whales) populations sharply declined in 2015, resulting in an ecosystem shift causing re-distribution of krill-predators. Humpback whales in the area were forced to expand their foraging grounds closer to the coast, nearer to commercial fishing gear (such as pot traps for the Dungeness crab fishery). Unfortunately, the marine heatwave and underlying ecosystem shifts (such as the Pacific Coast Domoic Acid Bloom) contributed to the increased occurrence of whale entanglements and strandings in the extreme northwest in 2015-16, including Alaska and British Columbia, Canada. 

Thankfully, NOAA satellites currently show that the Pacific Ocean is near pre-Blob temperatures and local agencies have reported a surge in krill and anchovy stock since 2016. Scientists are anticipating the ecosystem will recover from The Blob's disruption, five years after it first took place; however, significant challenges still lie ahead. In late 2019 and early 2020, there has been an increase in beached whale sightings on the Pacific coastline- NOAA has recorded 123 gray whale strandings in 2019, with several more recorded by unaffiliated sources in 2020. 

A graph
The marine heatwave that has formed off the West Coast of North America is currently close to the warmest area in the Pacific Ocean. Map shows sea surface temperature anomalies, with darker orange representing temperatures farther above average. Image from NOAA National Environmental Satellite, Data, and Information Service.

NOAA research scientists, such as Jarrod Santora, are using satellites and ecosystem survey data to develop a Habitat Compression Index (HCI) (link to the Nature article co-authored by Santora), which monitors the cool upwelling habitat area and its link to whale-entanglement risk in commercial fisheries. Simply put, warmer temperatures altered krill and anchovies populations and their distribution, causing whales to concentrate within a smaller area. While some whale species are experiencing a population resurgence, whales, in general, are still considered threatened or endangered. In the meantime, satellite-based metrics and ocean models are being used to better visualize sea surface developments and their potential ecological significance to whales and commercial fisheries.